Generally, an injection apparatus for a molding machine moves an injection plunger forward in a sleeve with an injection cylinder and forces molding material (e.g., molten material) out of the sleeve into a cavity formed between molds (mold unit) to inject and fill the molding material into the cavity. The injecting and filling operation includes a low speed operation, a high speed operation, and a pressurizing operation.
The injection apparatus performs the high speed operation by, for example, supplying hydraulic oil, which is accumulated in an accumulator, to the injection cylinder, and moving a rod (piston) of the injection cylinder at a high speed. Generally, in the high speed operation, a control valve controls an open degree of an oil passage connected to the accumulator to restrict movement of the rod and control the movement speed of the rod.
In the high speed operation, it is desirable that the injection time be further shortened. The response in the movement of the rod needs to be increased to shorten the injection time. To improve the response in the movement of the rod, the hydraulic pressure and the flow rate of the hydraulic oil acting on the piston need to be increased. The control valve, however, gradually opens the oil passage, and the hydraulic pressure acting on the piston is gradually increased. Thus, there is a limit to increasing the response in the movement of the rod.
The rod may be mechanically coupled to restrict movement of the rod when the hydraulic pressure of the hydraulic oil is acting on the piston. Under this situation, the mechanical coupling may be released to move the piston with the maximum hydraulic pressure. To implement such a structure, a connection mechanism that may be mechanically connected to and disconnected from the rod is required.
Patent document 1 describes a hydraulic clamp as an example of such a connection mechanism. As shown in FIG. 8, in the hydraulic clamp 80 of patent document 1, a hydraulic cylinder 81 includes a lower portion that accommodates a piston 82, which is movable in the vertical direction. A clamp hydraulic oil chamber 83 is defined at the lower side of the piston 82. In the hydraulic cylinder 81, an oil supply/discharge port 81a is formed below the clamp hydraulic oil chamber 83. Hydraulic oil from a hydraulic source 84 is supplied to and discharged from the oil supply/discharge port 81a through an electromagnetic supply/discharge valve 85 and a supply/discharge oil passage 86.
In the hydraulic cylinder 81, a clamp tool 87, which is formed by combining a plurality of clamp jaws 87a, is set on the upper surface of the piston 82. A retraction means (not shown) urges the clamp jaws 87a in directions enlarging the diameter. A tubular advancing inclination cam 88 is arranged at the upper side of the clamp tool 87. In an upper portion of the hydraulic cylinder 81, a pneumatic cylinder 90 is arranged above the clamp tool 87, and a pneumatic piston 91 of the pneumatic cylinder 90 surrounds the clamp tool 87.
A pneumatic operation chamber 92 is formed in the lower side of the pneumatic piston 91. A piston recovery spring 93 is arranged inside the pneumatic piston 91. The advancing inclination cam 88 is inserted into a piston rod 91a extending from the pneumatic piston 91 toward the clamp tool 87. An unclamp piston 99, movable in the vertical direction, is accommodated in the pneumatic operation chamber 92.
The hydraulic cylinder 81 includes a compressed air supply/discharge port 81b, which is in communication with the pneumatic operation chamber 92. Compressed air from a pneumatic source 94 is supplied to and discharged from the compressed air supply/discharge port 81b through an electromagnetic pneumatic supply/discharge valve 95 and a supply/discharge air passage 96.
The hydraulic clamp 80 sets the hydraulic cylinder 81 onto the clamp rod 97 from above and clamps the clamp rod 97 clamped with the clamp tool 87 to mechanically connect the hydraulic clamp 80 and the clamp rod 97. The clamp rod 97 includes a distal end defining a passive portion 97a that engages with the clamp tool 87.
To clamp the clamp rod 97 with the hydraulic clamp 80, the electromagnetic pneumatic supply/discharge valve 95 is controlled to discharge compressed air out of the pneumatic operation chamber 92. This moves the pneumatic piston 91 toward the advancing inclination cam 88 with the spring force of the piston recovery spring 93. This moves the advancing inclination cam 88 downward and reduces the diameter of the clamp tool 87 so that the clamp tool 87 is arranged facing the lower surface in the passive portion 97a of the clamp rod 97. When the hydraulic oil from the hydraulic source 84 is supplied to the oil supply/discharge port 81a, the clamp tool 87 moves upward as the piston 82 moves upward, and the distal end of the clamp tool 87 is pushed against the lower surface of the passive portion 97a. As a result, the clamp rod 97 is clamped by the hydraulic clamp 80, and the clamp rod 97 and the hydraulic clamp 80 are mechanically connected.
When the pressure oil is discharged from the oil supply/discharge port 81a and the compressed air is supplied to the pneumatic operation chamber 92, the piston 82 is moved downward by the unclamp piston 99. Further, the pneumatic piston 91 moves upward. Thus, the clamp tool 87 unclamps the clamp rod 97. That is, the clamp rod 97 and the hydraulic clamp 80 are mechanically disconnected.
The use of the hydraulic clamp 80 in the injection cylinder allows for the rod to be mechanically connected to and disconnected from the hydraulic clamp 80. This improves the response for moving the rod of the injection cylinder and allows for an increase in the injection speed during the high speed operation.